Cohesion and Adhesion in High Polymers

Indian Plywood Industries Research Institute Field Stat1on, Calcutta-700 061. Recent developments in polymers show that they are in a position to replace metals, particularly for articles of light weight, if their services are rendered in the temperature range between 50 and 300°. Organic polymers of tensile strength upto 500,000 p.s.i. can be made possible. Quality steels are still about four to five times stronger ; but if one compares the strength on the basis of equal weight, the polymers can ever be superior to metal since their specific gravity is much less in comparsion to the metals. If we analyse the situation since the introduction of the synthetic polymers, we would observe that the two principal factors which lead to superior mechanical strength of polymers are : (i) introduction of new materials with new chemical compositions, and (ii) improvement of the molecular organisation of the given material. Although the rayon tire cord still consists or the same cellulose, the higher tensile strength of the material has been achieved due to the higher molecular weight and better molecular and fibrillar organisation of the product. The improved impact strength of polystyrene has been accomplished by the .introduction of additional monomer-acrylonitrile or butadiene or both-so that the new materials consist of a copolymer of two or more individual ingredients. It has been realised that natural products used as adhesives by our ancestors are polymeric in nature ; in fact most adhesives used at presentare polymers of one sort or another